For the purpose of accurately obtaining a reference position at which a brake disc (also referred to as brake rotor) and a brake pad begin to contact with each other, the following is described in an existing art.
In Patent Document 1, it is described that an electric drive braking system includes a differentiating circuit for an output of a press sensor and a circuit that compares a differential value with a set threshold and then sets an origin point (reference position) to a position at which the differential value of the output of the press sensor becomes lower than the set threshold.
In Patent Document 2, it is described that, in an electric brake, when a pressing force that is applied to a brake pad is reduced, the rotation position of an electric motor at the time when the gradient of reduction in pressing force (a variation in pressing force to a variation in rotation angle) becomes gentler than a set gradient, is set for a temporary zero-point position, and a position shifted to the back side from the temporary zero-point position by an amount α corresponding to a non-reset amount of the brake pad is set to a zero-point position (reference position).
In Patent Document 3, it is described that, at the time of releasing a brake, a position at which a piston is returned from a piston position at the time when a piston thrust becomes smaller than or equal to a predetermined threshold larger than zero to a brake releasing side by a predetermined amount is set for a contact start position (reference position) at which a disc rotor and a brake pad begin to contact with each other.